As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, much research has focused on lithium secondary batteries having high energy density and discharge voltage. Such batteries are commercially available and widely used.
Generally, as cathode active materials for lithium secondary batteries, lithium-containing cobalt oxides such as LiCoO2 are mainly used. In addition thereto, use of lithium-containing manganese oxides such as LiMnO2 having a layered crystal structure, LiMn2O4 having a spinel crystal structure, and the like and lithium-containing nickel oxides such as LiNiO2 is also under consideration.
Among cathode active materials, LiCoO2 is widely used due to excellent overall physical properties such as excellent cycle properties, and the like. However, LiCoO2 is low in safety and expensive due to resource limitations of cobalt as a raw material. Lithium nickel based oxides such as LiNiO2 are cheaper than LiCoO2 and exhibit high discharge capacity when charged to a voltage of 4.25 V. However, lithium nickel based oxides have problems such as high production cost, swelling due to gas generation in batteries, low chemical stability, high pH and the like.
In addition, lithium manganese oxides, such as LiMnO2, LiMn2O4, and the like, are advantageous in that they contain Mn, which is an abundant and environmentally friendly raw material, and thus are drawing much attention as a cathode active material that can replace LiCoO2. In particular, among the lithium manganese oxides, LiMn2O4 has advantages such as a relatively cheap price, high output and the like. On the other hand, LiMn2O4 has lower energy density, when compared with LiCoO2 and three component-based active materials.
To overcome these drawbacks, some Mn of LiMn2O4 is substituted with Ni and thereby LiMn2O4 has a higher potential (approximately 4.7 V) than original operating potential (approximately 4 V). Due to the high potential, a spinel material having a composition of Li1+aNixMn2−xO4−z (0≦a≦0.1, 0.4≦x≦0.5, and 0≦z≦0.1) is well suited to use as a cathode active material of EVs, and medium and large lithium ion batteries requiring high energy and high-output performance. However, due to high charge and discharge voltage potential, there are a variety of problems, which must be solved, such as reduced battery performance caused by Mn dissolution of the cathode active material and side reaction of an electrolyte.
Meanwhile, in case of a lithium transition metal active material containing two or more materials such as Ni, Mn and the like, as described above, it is not easy to synthesize the lithium transition metal active material through a simple solid-phase reaction. Thus, as a precursor for preparing the lithium transition metal active material, use of a transition metal precursor prepared using a co-precipitation method or the like is known.
To solve the above problems and exhibit desired performance by preventing tap density reduction and optimizing a particle shape such as a globular shape or the like through control of a particle size or the like of such a transition metal precursor, by uniform precipitation, and the like, research into lithium transition metal oxides is underway.
A precursor having high tap density by controlling particle sizes and particle distribution may be synthesized, and a particle shape such as a globular shape may be optimized. Furthermore, the lithium composite transition metal oxide as described above may exhibit superior performance as a cathode active material
However, despite such various tries, a precursor for preparing a lithium composite transition metal oxide having satisfactory performance and a lithium composite transition metal oxide obtained therefrom have yet to be developed.